Reduction of emission of carbon dioxide (CO2 gas) as greenhouse gases has been recently becoming a global problem, and the reduction of emission of carbon dioxide has been also strongly required to vehicles as emission sources of carbon dioxide. Therefore, the friction between a sliding member and a sliding target member as a partner member to the sliding member in a vehicle is reduced. For example, it has been proved that enhancement of fuel consumption, prevention of baking and prevention of occurrence of abnormal sounds can be performed by subjecting the sliding face of a piston (sliding member) of an internal combustion engine to a surface treatment.
As this type of surface treatment method has been proposed a method of impregnating a base member of aluminum (containing aluminum alloy) with chemical conversion treatment liquid containing etching liquid and water-soluble metallic salt (for example, silver) to conduct a surface roughening treatment on the surface of the aluminum base member with this etching liquid and substantially simultaneously form metallic coating on the surface of the aluminum base member with metal composing the water-soluble metallic salt (see Patent Document 1, for example).